In September, 2020, the EPA released “a proposal to improve current resistance management strategies for certain Lepidopteran pests of Bacillus thuringiensis (Bt) plant-incorporated protectants (PIPs) in corn and cotton. EPA is soliciting input from all affected stakeholders such as corn and cotton growers, crop consultants, industry, academia, non-governmental organizations and the general public.”

The following excerpt delineates the agency’s concerns about resistance, it’s plans to improve management as well as additional measures that are being considered:

EPA is concerned about recent cases of Bt resistance among corn and/or cotton pests that have been documented by academic and industry researchers. Bt resistance has been reported for corn earworm, fall armyworm, western bean cutworm, and southwestern corn borer. In a white paper prepared for the SAP meeting, EPA identified a number of risk factors that likely contributed to these resistance cases and could lead to more widespread resistance incidents in the future. These risk factors include a lack of “high dose” toxin expression in Bt PIPs for some of the Lepidopteran target pests, cross resistance between different Bt PIPs, cross-pollination of Bt and refuge plants in Bt corn seed blend products, poor compliance with non-PIP refuge requirements, and ineffective resistance monitoring methods. Seeking guidance on these concerns, the Agency convened a FIFRA SAP meeting in July 2018. The panel was tasked with evaluating the reported cases of resistance and EPA's identified risk factors and providing guidance on potential improvements to the current resistance management program. Meeting materials, including EPA's white paper, the charge to the panel, and the SAP's final report, are available in docket number EPA-HQ-OPP-2017-0617.

Following the SAP meeting, EPA developed a proposal to bolster current resistance management strategies for Lepidopteran target pests of Bt corn and cotton PIPs. EPA's proposal addresses the following aspects of resistance management:

  • A proposed new resistance definition for “non-high dose” Lepidopteran pests, based on unexpected injury (UXI) levels in Bt corn and cotton;
  • Enhanced resistance monitoring using sentinel plots in regions at high risk of resistance and investigations of UXI cases with standardized pest damage thresholds;
  • Improved resistance mitigation for cases of confirmed resistance by implementing best management practices (BMPs) once UXI has been detected;
  • Increased communications among stakeholders to provide “early warnings” on potential cases of resistance to Bt PIPs;
  • Industry reporting to EPA on UXI investigations and BMP implementation.

In addition to the above elements, EPA has identified three further measures for public comment, but will not take a position on them until it has reviewed all stakeholder input:

  • Phase down of single traits and non-functional pyramids;
  • Increasing percent refuge in seed blend products; and
  • Measures to improve refuge compliance.

The Agency is seeking input on the proposal from potentially affected entities and other stakeholders, including (but not limited to) registrants of Bt PIPs, corn and cotton growers, crop consultants/agronomists, commodity groups, extension entomologists, academic researchers, and the general public. Commenters are also encouraged to provide input on the specific recommendations of the SAP, including alternate approaches or counter proposals towards addressing the issues raised by the panel and the Agency's resistance management goals. During the comment period, EPA will seek to further engage affected entities and other stakeholders through webinars in late July and August to discuss the proposal and answer questions.

The entire draft proposal (downloadable PDF) can be found here.

Bolstering the management practices would no doubt be beneficial for managing Bt resistance. The further measures for which the EPA is seeking comment — especially the “phase down of single traits and non-functional pyramids” — is a concern for growers as it could potentially eliminate or restrict a large number of available seed options from the marketplace. In fact, if all the corn hybrids and cotton varieties that have documented resistance were to be phased down, only those containing Syngenta’s Vip3A protein would be unaffected. Check out the trait tables from Texas A&M to get a better understanding of which Bt proteins are in the corn trait packages currently on the market.

Farmers have until Nov. 7, 2020, to comment on the EPA proposal.